Assignment_6_JH_GE
Jon Hart & Garrett Eyer
Introduction
Figure 1. Pacific Giant Salamander (Credit: Sierra Nystrom)
Figure 2. The Mack Creek study site is located in the HJ Andrews Experimental Forest, Oregon. (Credit: Dana Warren)
Figure 3. Mack Creek, HJ Andrews Experimental Forest, OR (Credit: Oregon State University)
Data and Methods
Results
| Channel Class | Clear Cut | Old Growth |
|---|---|---|
| Cascade | 444 (54%) | 377 (46%) |
| Pool | 101 (44%) | 129 (56%) |
| Side Channel | 130 (55%) | 107 (45%) |
##
## Pearson's Chi-squared test
##
## data: chi_sal_counts
## X-squared = 8.1429, df = 2, p-value = 0.01705There IS a significant effect of forest condition (old growth/clear cut) on where in the channel salamanders are found (pool/side-channel/cascade) for salamanders sampled in 2017. (\(\chi\)2(2) = 8.14, p = 0.017).
##
## Welch Two Sample t-test
##
## data: weight_ttest_og and weight_ttest_cc
## t = -3.5793, df = 1292.1, p-value = 0.0003573
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
## -2.7890718 -0.8141428
## sample estimates:
## mean of x mean of y
## 6.412422 8.214030##
## Cohen's d
##
## d estimate: 0.196305 (negligible)
## 95 percent confidence interval:
## lower upper
## 0.08798274 0.30462734Mean Pacific Giant Salamander size in the clear cut section of Mack Creek in 2017 (8.21 \(\pm\) 9.97, n = 675) differed significantly from mean Pacific Giant Salamander size in the old growth section of Mack Creek in 2017 (6.41 \(\pm\) 8.27, n = 644) by a two-sided, two sample t-test (t(1292.14) = -3.58, p < 0.001. Although there is a stastitical difference in mean size among salamanders in different forest conditions, the effect size is negligible (Cohen’s d = 0.2).
## Levene's Test for Homogeneity of Variance (center = median)
## Df F value Pr(>F)
## group 2 15.111 3.263e-07 ***
## 1283
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1Does not satisfy assumptions for ANOVA test?
Summary
References
Gregory S. V. 2016. Aquatic Vertebrate Population Study in Mack Creek, Andrews Experimental Forest, 1987 to present. Environmental Data Initiative. https://doi.org/10.6073/pasta/5de64af9c11579266ef20da2ff32f702. Dataset accessed 11/27/2019.